“A man with a conviction is a hard man to change. Tell him you disagree and he turns away. Show him facts or figures and he questions your sources. Appeal to logic and he fails to see your point.”
Leon Festinger developed the theories of cognitive dissonance and social comparison. Cognitive dissonance is the state of discomfort you feel when you hold two conflicting beliefs. You may smoke even though you know it is bad for your health. His social comparison theory says that you evaluate your ideas by comparing them with what other people believe. You are also more likely to seek out other people who share your beliefs and values.